如何制作带有初始文本“Select One"的Android Spinner?

How to make an Android Spinner with initial text quot;Select Onequot;?(如何制作带有初始文本“Select One的Android Spinner?)

问题描述

我想使用最初(当用户尚未做出选择时)显示文本选择一个"的 Spinner.当用户单击微调器时，将显示项目列表并且用户选择其中一个选项.用户做出选择后，所选项目会显示在 Spinner 中，而不是Select One".

I want to use a Spinner that initially (when the user has not made a selection yet) displays the text "Select One". When the user clicks the spinner, the list of items is displayed and the user selects one of the options. After the user has made a selection, the selected item is displayed in the Spinner instead of "Select One".

我有以下代码来创建 Spinner:

I have the following code to create a Spinner:

String[] items = new String[] {"One", "Two", "Three"};
Spinner spinner = (Spinner) findViewById(R.id.mySpinner);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_spinner_item, items);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);

使用此代码，最初会显示项目One".我可以在项目中添加一个新项目Select One"，但随后Select One"也会作为第一项显示在下拉列表中，这不是我想要的.

With this code, initially the item "One" is displayed. I could just add a new item "Select One" to the items, but then "Select One" would also be displayed in the dropdown list as first item, which is not what I want.

我该如何解决这个问题?

How can I fix this problem?

推荐答案

这是一个覆盖 Spinner 视图的通用解决方案.它覆盖 setAdapter() 以将初始位置设置为 -1，并代理提供的 SpinnerAdapter 以显示位置小于 0 的提示字符串.

Here's a general solution that overrides the Spinner view. It overrides setAdapter() to set the initial position to -1, and proxies the supplied SpinnerAdapter to display the prompt string for position less than 0.

这已经在 Android 1.5 到 4.2 上进行了测试，但买家要小心！由于此解决方案依赖反射来调用私有 AdapterView.setNextSelectedPositionInt() 和 AdapterView.setSelectedPositionInt()，因此不能保证在未来的操作系统更新中正常工作.看起来很可能会，但绝不能保证.

This has been tested on Android 1.5 through 4.2, but buyer beware! Because this solution relies on reflection to call the private AdapterView.setNextSelectedPositionInt() and AdapterView.setSelectedPositionInt(), it's not guaranteed to work in future OS updates. It seems likely that it will, but it is by no means guaranteed.

通常我不会宽恕这样的事情，但这个问题已经被问了足够多的时间，而且我认为我会发布我的解决方案似乎是一个足够合理的要求.

Normally I wouldn't condone something like this, but this question has been asked enough times and it seems like a reasonable enough request that I thought I would post my solution.

/**
 * A modified Spinner that doesn't automatically select the first entry in the list.
 *
 * Shows the prompt if nothing is selected.
 *
 * Limitations: does not display prompt if the entry list is empty.
 */
public class NoDefaultSpinner extends Spinner {

    public NoDefaultSpinner(Context context) {
        super(context);
    }

    public NoDefaultSpinner(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public NoDefaultSpinner(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public void setAdapter(SpinnerAdapter orig ) {
        final SpinnerAdapter adapter = newProxy(orig);

        super.setAdapter(adapter);

        try {
            final Method m = AdapterView.class.getDeclaredMethod(
                               "setNextSelectedPositionInt",int.class);
            m.setAccessible(true);
            m.invoke(this,-1);

            final Method n = AdapterView.class.getDeclaredMethod(
                               "setSelectedPositionInt",int.class);
            n.setAccessible(true);
            n.invoke(this,-1);
        } 
        catch( Exception e ) {
            throw new RuntimeException(e);
        }
    }

    protected SpinnerAdapter newProxy(SpinnerAdapter obj) {
        return (SpinnerAdapter) java.lang.reflect.Proxy.newProxyInstance(
                obj.getClass().getClassLoader(),
                new Class[]{SpinnerAdapter.class},
                new SpinnerAdapterProxy(obj));
    }



    /**
     * Intercepts getView() to display the prompt if position < 0
     */
    protected class SpinnerAdapterProxy implements InvocationHandler {

        protected SpinnerAdapter obj;
        protected Method getView;


        protected SpinnerAdapterProxy(SpinnerAdapter obj) {
            this.obj = obj;
            try {
                this.getView = SpinnerAdapter.class.getMethod(
                                 "getView",int.class,View.class,ViewGroup.class);
            } 
            catch( Exception e ) {
                throw new RuntimeException(e);
            }
        }

        public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
            try {
                return m.equals(getView) && 
                       (Integer)(args[0])<0 ? 
                         getView((Integer)args[0],(View)args[1],(ViewGroup)args[2]) : 
                         m.invoke(obj, args);
            } 
            catch (InvocationTargetException e) {
                throw e.getTargetException();
            } 
            catch (Exception e) {
                throw new RuntimeException(e);
            }
        }

        protected View getView(int position, View convertView, ViewGroup parent) 
          throws IllegalAccessException {

            if( position<0 ) {
                final TextView v = 
                  (TextView) ((LayoutInflater)getContext().getSystemService(
                    Context.LAYOUT_INFLATER_SERVICE)).inflate(
                      android.R.layout.simple_spinner_item,parent,false);
                v.setText(getPrompt());
                return v;
            }
            return obj.getView(position,convertView,parent);
        }
    }
}

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